<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body{
            margin: 0;
        }
        #left{
            width: 200px;
            height: 500px;
            background: #ccc;
            /* float: left; */
        }
        #right{
            height: 500px;
            background: #f00;
            /* margin-left: 210px; */
            /* position: relative;
            top: -500px; */
            position: absolute;
            left: 210px;
            top: 0;
            right: 0;
        }
    </style>
</head>
<body>
    <div id="left">left</div>
    <div id="right">right</div>
</body>
</html>